Interpretive Summary: Elemental iron powders are widely used to fortify flour and cereal products. Our objective was to test the hypothesis that baking enhances the bioavailability of elemental iron powders by oxidizing the iron. In the present study we used a simulated digestion/cell culture model and a piglet model to measure bioavailability of the Fe. Bread flour, either unfortified or fortified with hydrogen reduced (HR) iron powder or FeSO4 (300 mg Fe/kg flour) was baked into bread. For the cell culture studies, bread samples were treated with digestive enzymes and placed on monolayers of cultured Caco-2 cells, a human intestinal epithelial cell line. Piglet diets containing 35% dried bread were prepared and fed in 2 studies. The rate of increase in hemoglobin Fe over the feeding period was used to calculate relative biological value (RBV), an index of iron bioavailability. Iron uptake by Caco-2 cells fed HR Fe bread was similar to cells fed FeSO4 bread for digests incorporating a pH 2 peptic digestion but lower for digests where the peptic phase was conducted at pH 3, 4, 5, 6, and 7 (P < 0.05). In the first pig study, RBV of HR Fe added to flour prior to baking was 47.9% when compared to FeSO4 fortified flour (P<0.05). In the second pig study, a 3rd treatment consisting of unfortified bread with HR iron added during diet mixing (after bread baking) was included. RBVs of the HR Fe diet (Fe added after baking) and HR Fe diet (Fe added before baking) were 40.0% and 53.2%, respectively, compared to the FeSO4 diet. Differences in RBV between the HR Fe (after baking) and FeSO4 (before baking) treatment groups were significant, but the difference between the before and after HR treatment groups was not significant. We conclude that bread baking does not enhance the bioavailability of elemental iron powders.

Technical Abstract:
Elemental iron powders are widely used to fortify flour and cereal products. Our objective was to test the hypothesis that baking enhances the bioavailability of elemental iron powders by oxidizing Fe0 to Fe2+ or Fe3+. In the present study we used an in vitro digestion/Caco-2 cell culture model and a piglet model to measure bioavailability. Bread flour, either unfortified or fortified with hydrogen reduced (HR) iron powder or FeSO4 (300 mg Fe/kg flour) was baked into bread. For the in vitro studies, bread samples were treated with digestive enzymes and placed on monolayers of cultured Caco-2 cells. Swine diets containing 35% dried bread were prepared and fed to cross-bred (Hampshire x Landrace x Yorkshire) anemic swine in 2 studies. The rate of increase in hemoglobin Fe over the feeding period was used to calculate relative biological value (RBV), an index of iron bioavailability. Iron uptake by Caco-2 cells fed HR Fe bread was similar to cells fed FeSO4 bread for digests incorporating a pH 2 peptic digestion but lower for digests where the peptic phase was conducted at pH 3, 4, 5, 6, and 7 (P < 0.05). In the first pig study, RBV of HR Fe added to flour prior to baking was 47.9% when compared to FeSO4 fortified flour (P<0.05). In the second pig study, a 3rd treatment consisting of unfortified bread with HR iron added during diet mixing (after bread baking) was included. RBVs of the HR Fe diet (Fe added after baking) and HR Fe diet (Fe added before baking) were 40.0% and 53.2%, respectively, compared to the FeSO4 diet. Differences in RBV between the HR Fe (after baking) and FeSO4 (before baking) treatment groups were significant, but the difference between the before and after HR treatment groups was not significant. We conclude that bread baking does not enhance the bioavailability of elemental iron powders.